Avoid specifying a key column in a double-link scenario

Question

Suppose I have the following two classes:

public class User : Entity
{
    public virtual IList<Item> Items { get; set; }
}

public class Item : Entity
{
    public virtual User Owner { get; set; }
}

I created two mapping classes:

public class UserMap : ClassMap<User>
{
    public UserMap()
    {
        Id(x => x.Id);
        HasMany(x => x.Items);
    }
}

public class ItemMap : ClassMap<Item>
{
    public ItemMap()
    {
        Id(x => x.Id);
        References(x => x.Owner);
    }
}

This will result in a table Itemthat has a column UserIdand a column OwnerId. When I use KeyColumn("OwnerId")for matching HasMany, it only works with the column OwnerId, but I would like to avoid it. Is there a way to tell NHibernate to use the column created by the mapping in ItemMap?

Why I don’t want to explicitly specify a column:
The column name is OwnerIdautomatically generated based on the property name and some rules. If I change either the rules or the property name, I need to remember to change this KeyColumn. So basically this is not save refactoring.

Answer 1

: ​​

,

public static void KeyColumnFromReference<TChild>(
    this OneToManyPart<TChild> collectionmap, ClassMap<TChild> map, Expression<Func<TChild, object>> referenceprop)
{
    string propertyname = GetPropertyName(referenceprop);
    var column = ((IMappingProvider)map).GetClassMapping()
        .References.First(m => m.Name == propertyname)
        .Columns.First().Name;

    collectionmap.KeyColumn(column);
}

public static void KeyColumnFromReference<T, TChild>(
    this OneToManyPart<TChild> collectionmap, ClassMap<TChild> map)
{
    var column = ((IMappingProvider)map).GetClassMapping()
        .References.First(m => m.Type == typeof(TChild))
        .Columns.First().Name;

    collectionmap.KeyColumn(column);
}

public UserMap()
{
    HasMany(x => x.Items)
        .KeyColumnFromReference<User, Item>(new ItemMap());

    // or

    HasMany(x => x.Items)
        .KeyColumnFromReference(new ItemMap(), u => u.Owner);
}

, IHasManyConvention EntityType propertyname ( ChildType)

Update:

class ForeignKeyConvention : IHasManyConvention
{
    public void Apply(IOneToManyCollectionInstance instance)
    {
        // to force the compiler to take the Name property and not the Name method
        string propertyName = ((ICollectionInspector)instance).Name;

        // should be equal to the convention for the reference key column
        instance.Key.Column(propertyName + instance.EntityType.Name + "id");
    }
}